Roman Military Diplomas / Diplomata (or better citizenship
and/or military discharge certificates) are in some way the "greencards"
of Roman times (green also being the dominating color of their bronze patina).
Only that today you can win citizenship in a lottery. In Roman times foreigners
had to serve for minimum 25 years (army) or 26 years (fleet) or longer
in the auxiliary military forces (infantry = cohors, infantry mixed
with light cavalry =cohors equitata, heavy cavalry = ala, fleet = classis,
or pretorian cohors). In contrast the Roman legions (up to ca. 30 elite units
mainly distributed along the borders of the empire, of ca. 5000 "legionaries"
each) were reserved for Roman citizens. This distinction is thought to have lost its importance
when Caracalla granted Roman citizenship in the early third century to
all living in the Roman empire (except to the slaves of course), known
as the Constitutio Antoniniana of 212 AD.

Roman Military Diplomas (more than 1000 are known to us and
published to date) were/are found all over the Roman empire, mostly but
not exclusively in the border provinces. As Diplomas show also the
origin of the recipient, we can see that the middle and lower
Danube region was a major recruitment area
for non-citizens into the Roman auxiliary forces in the first and
second
century AD. While some veterans seem to have stayed close to their last
place of service, many veterans - especially from the Danube region - seem to have
returned to their
home provinces after serving all over the vast Roman empire (we can
conclude that from diplomas whose find spot is known). But there is no
clear rule, a diploma could be found anywhere in the Roman empire,
regardless of place of origin or service.

The massive
barbaric invasions in the third century AD destroyed many Roman
settlements, some
never to be inhabited again, thus conserving diplomas that would
otherwise
have been melted down eventually for their metal value. Still only a
fraction of < 1% of issued diplomas seems to have survived.

What is a Constitution ?

A constitution is a legal document issued by the
Emperor in Rome. In case of Roman Military Constitutions the emperor granted Roman citizenship
to specific veterans and their families, after a long and honorable service.

The legal process is thought to have been...:
1) The office of the Commander of an auxiliary unit lists all
those soldiers of his ala or cohors ready for retirement or deserving citizenship
2) He sends the list to the governor of his province
3) The provinical governor's administration bundles
all such requests for that province
4) and sends the list for this province to Rome
5) The imperial administration office in Rome draws up
an imperial constitution for that province to grant citizenship to all
the veterans on the list
6) The emperor personally approves and grants the
rights
7) A large bronze plate is written up listing all included veterans and placed
publically in Rome (ie at the Minerva Statue
behind the Divus Augustus Temple)
8) Individual bronze copies (diplomas) are written
in Rome for each veteran with his name (possibly but not likely at cost of the veteran)
9) The copies are checked, confirmed, wired, and
sealed by 7 witnesses
10) The diplomas are sent to the governor in the
province (more likely than sending them straight to the unit)
11) Diplomas for a specific unit are sent on from
the Provincial capital to the unit commander
12) The unit commander hands out the diplomas to the
veterans (likely in some sort of a ceremony)

We have published recently a diploma from an auxiliary
constitution issued for only two veterans, a centurio and a horse soldier
! But mostly we are talking of veterans from anywhere between ca. 4 and ca. 25
auxiliary units, depending on the specific need of that province at that
time. Sometimes more then one constitution was issued for the same province
at the same date (split by units for logistical reasons ?). Thus potentially
hundreds of soldiers at a time. Same for a praetorian fleet.

How many diplomas would have been issued for a given
unit on a single date ? Let us take a regular cohors, 500 men, each serving
25 years. That would be 20 veterans each year assuming yearly recruitment
(not always the case, see below) and no deaths (depends on circumstances).
Or 40 in a milliaria unit of 1000 men. More real life scenarios show
however that a major crisis like the Bar Kochba uprising caused major casualties,
mass recruiting shortly after to fill the ranks, and multiple diplomas
ie for the neighbouring province of Syria 25 years later. In similiar
circumstances we know of 10 or more diplomas surviving of the same constitution
indicating such a massive "bolus" of discharge.

A constitution could have covered thus between one
and several hundred soldiers.

Constitutions are known to us only through their
personalized copies = diplomas. Not a single of the large bronze plates
from Rome survived. Below image shows a possible fragment of a constitutional
tabula from Rome listing all the soldiers of a province that received Roman
citizenship. It was re-used as a military diploma later on. (The "new"
side with the diploma text not shown)

Possibly
the only surviving fragment of a constitutional tabula (re-used on the
other side as a military diploma later on), Weissenburg Museum, Germany

How many constitutions do we know ? More than 400
Constitutions have been identified to date, with more than 1000 surviving individual military
diplomas, some complete, but most in small fragments.

Which Units Received Citizenship Constitutions ? How many do we know ?

Constitutions cover mainly auxiliary forces and provincial
fleets for non-citizen troops based along the the frontier. Survival of diplomas is more likely in provinces
with many units - we only see a small fraction of what has been issued
back then, maybe as little as 0.3 %, which is not surprising considering
that bronze was a valuable and easily re-usable resource. For example we know more constitutions for Moesia
(inferior and superior), Pannonia (inferior and superior), Dacia, Raetia, Germania, Britannia,
and Mauretania Tingitana than for provinces with only small military presence such Thracia or Sardinia.

Constitutions are also known for the
praetorian cohorts, the emperor's horse guard, and for the praetorian fleets
in Ravenna and Misene. Below
two graphs showing all known Roman citizenship constitutions as of
December 31, 2014, first for the provinicial auxiliary forces incl the
Equites singulares, and in the second graph the Fleets, the Praetorian
and Urban Cohorts:

The graphs below are from 2006 and have not been
updated, but the relative survival rates have not changed dramatically
despite the new material published, what was common then is still
common, what was rare then is still rare.

as of 2006

The earliest known diplomas are from the reign of
Claudius, the latest of the Tetrarchy. Most common are those of Antoninus
Pius, also Traianus, and Hadrianus (see below graph). Bronze diplomas were
found for almost every year between the middle of the 1st century and mid
3rd century AD. We know however of two periods, one during the Germanic
invasions under Marcus Aurelius and the other during the crisis after Gallienus
to the Tetrarchy, where not a single (bronze) diploma survived. Why ? Werner Eck,
David Macdonald, and I have speculated in a recent article that this could be
due to bronze having been too costly in these periods of crisis, possibly
combined with less discharges due to a high number of casualties in war
and disease like the plague epdiemic reported in that period. Thus the
practice of issuing constitutions and diplomas would have continued, but
less being issued and on other perishable materials. We know ie of certain
privileges to soldiers found in Egypt written on wood or papyrus. But if
these were official documents like a bronze diploma remains unclear. Still
the hypothesis that the issue of diplomas was a regular process, for all
provinces, every year as needed, and for all veterans, is making a lot
of sense.

as of 2006

What does a Roman Military Diploma look like ?

A complete diploma consists of 2 bronze plates of
rectangular shape, between 10x12 and 21x16 cm depending on the period,
with text on both sides, bound together by bronze wire and sealed with
witnesses seals. The seals were covered by three bronze strips to protect
them from mechanical wear.

Below a typical diploma, unwired
and opened up, with preserved witness seals and their protecting metal
cover (closed and opened). This particulary well preserved example was
found in Slavonski
Brod and had been issued under Vespasianus.

The outer side of the so called tabula
1 holds a copy of the complete text. The outer side of tabula 2 (right)
lists the seven witnesses and holds the seals.

(The images below are from the Slavonski Brod Website).

Below image shows the seals exposed

The two inner sides of the two tabulae
together reflect the outer text of tabula I, sometimes abbreviated and
often the text is written less carefully than on the outer sides. There
is the hypothesis that the actual copy of the Constitution in Rome is the
inner - protected and sealed - text, while the outer text was for daily
use. The fact that the inner text got more and more neglected shows that
this seems to have been forgotten over time, maybe because the inner text
was rarely ever exposed

Another complete auxiliary diploma,
still wired together (seals and their cover are lost)From MARCUS AURELIUS & his son
COMMODUS, 23 March, 178 A.D., under the consulship of Sergius Scipio Orfitus
and P. Velius Rufus, Britannia under the governor Ulpius Marcellus, to
the cavalryman Thiophorus, a Dacian of the VII Thracian cohort, under the
command of Ulpius Marcianus. (from the Axel Guttmann collection)

Why twice the same text ? The outer side was for
daily use. If there was any suspicion of fraud, Roman provincial officials
could break the seals and compare the outer with the inner text, compare
for manipulations without having to wait for confirmation from far away
Rome. Suetonius describes this practice for important documents in the
Nero text of his 12 Caesars Book.

The thickness and weight of diplomas differs considerably,
as does their size. Early and late pieces are usually thicker and heavier,
and more carefully written. Under Antoninus Pius, with the quantity of
known diploma reaching a peak, the quality seems to have deteriorated.
Late diplomas are occasionally made from pre-used bronze plates, the original
text still being visible in traces.

Diplomas were handed out to the veteran in his province
as proof of his honorable service, his newly granted Roman citizenship
for himself and his children. One cannot rule out that the veteran had
to pay for his bronze diploma, and that not all veterans were willing or
able to do so. But there is no indication at all that this may have been
the case. And considering the central importance of the army and the fact
that this privilege was given after a lifetime of honorable service, I
personally see no reason not to believe the emperor took care of the cost
for bronze. Still the fact that we find more diplomas for horse soldiers
- presumably better paid - could be indicative for this hypothesis. But
maybe horse soldiers simply had a better chance for survival ?

What is the Legal Text ?

All diplomas follow the same scheme, with sectors
of standard legal text and sectors with individualized text.

"EQVITIBVS ET PEDITIBVS QVI MILITAVERVNT IN ALIS...
ET COHORS...." followed by a list of alae and cohorts with their numerals
& names (e.g. "...ET III GALLica...") that discharged veterans at this
moment (up to some 25 units listed)

The province and the governor:

"...ET SVNT IN..." Province Name "...SVB..." Governor
Name "

Citizenship legal text (varied over the centuries):

Legal standard text over several lines describing
the reason for (...DIMISSIS HONESTA MISSIONE... DVMTAXAT SINGVLI SINGVLAS)
and the conditions of the citizenship. 25 years of service were required
for auxiliary units

Below an example of an inner text of
a tabula II from the Munich Archeological Museum, for the Helvetian soldier
Cattus, son of Bardus, and his wive Sabina, his son Vindelicus, and his
daughter Materiona:

The date (day and month) and the year are defined
by the two consules - though to reflect the day of issue of the diploma:
Ie in the above example A D XVII K IVLIAS,
C LAECANIO BASSO, M LICINIO CRASSO FRVGI COS

Dates were counted as days before specific
days in the Roman calendar. K stands for the Kalendae and means the first
day of a month, ID for Idus and means the 13th of each month (the 15th
in March, May, July, and October), N stands for Nonae, the 5th day of each
month (the 7th in March, May, July, and October). AD PR K AVG would
thus mean the day before the first of August = the 31 of July. And we still
use the same names for the months today.

In addition the years were defined by the consuls.
Ordinary consuls are the consuls elected for the first months of a year,
followed by several pairs of suffect consules. All consul pairs were listed
in the list of consuls and thus defined a given year.

Recipient part of the diploma:

Name of the unit the soldier had last served
in (one of those units listed in the text above). In this example from
the Ala Gemelliana

Name of the commander of this unit, sometimes his
origin, here Q POMPONIVS Q F COL RVFVS

Name of soldier, his father, his origin in the above
example a soldier from the Helvatian Tribe

Name of his wife, her father, her origin (if
applicable)

Name of their children, sons and daughters (if
applicable and diploma issued before ca. 140 AD)

Legal text stating that this is a witnessed copy of
the original constitution in Rome:

"DESCRIPTVM ET RECOGNITVM..." Written
and confirmed from the orginal bronze plates who are stored in Rome behind
the Augustus Temple at the Minerva statue.

Fleet
Diplomas:Similiar to above, just that there is obviously
no list of units, but only the name of the fleet. The commander of the
fleet replaces the governor, sometimes the name of the captain of the ship
is mentioned as commander of the unit. 26 years of service, later more
was required.

Another still wired diploma, shown
is the side with the witnesses (Munich Archeological Museum)

What was the Importance of the Diploma for
the Veteran's Family ?

Auxiliary diplomas from Claudius to the early 140s
also name the veterans wives and kids if they had any and the legal text
covers not only the veteran, getting Roman citizenship, but also his family.

Legal constraints need to be considered here:

Roman soldiers (legionaries and auxiliaries) could
not get married during their military service, and mostly they were too
young when enlisted to already be married. From Septimius Severus onwards
marriage during the service seems to have been allowed.

Non-Roman Citizens could only join the Auxiliary forces,
the Praetorian Fleets, and the Praetorian Cohorts, but not the Roman legions
who were restricted to Roman Citizens. Major recruiting grounds for the
legions seem to have been Italy, Spain, and also Gaul from which we find
very few auxiliaries mentioned on diplomas. Major recruiting grounds for
the auxiliary forces were the Balkans (Dacians, Tracians, Erovisci, Pannonians,
etc), but also Northern Africa and Syria. Through Caracalla’s widening
of the citizenship all these areas are thought to have received Roman
citizenship.

Roman citizens could not legally marry non-citizen
women (foreigners, slaves, Iunian status women), creating issues once an
auxiliary got Roman citizenship at the end of his 25 year service. Equally
for a legionary who partnered with a non-citizenship woman.

Children from such an illegal relationship were not
Roman citizens and could not fully inherit from their father

The Veteran received however in the diploma the right
to marry officially (conubium) a foreign woman without Roman citizenship
(but only one and only once). The veteran's possible inoffical liaison
with such a woman was thus legalized, she herself did not get Roman citizenship.
Such women can be found on diplomas with their father's name and their
place of origin. For unknown reasons very few wives are specifically mentioned
on auxiliary diplomas after the early 140s, maybe because more and more
veterans were able to marry Roman citizens even in the provinces, offspring
from other veteran families.

Children to such an inofficial relationship
were only named on diplomas until ca. 140 AD, afterwards only children
born after the military service were included in the legal text
(but of course were born too late to be named on the diploma). As exception
to the rule we still -rarely- find diplomas with special legal formulas
that continue to name wives and kids, but only for officers
(centurios or decurios) with families they had "registered" with the governor
before they entered service. After their service they then got the privileges
and the kids were named on the diploma. There is strong evidence that this
privilege was not always restricted to officers, but also offered to common
soldiers. Not many cases though, most common soldiers will have been too
young anyway when enlisting to have qualifying families.

And we know of at least one diploma where Roman
citizenship was also granted to the parents and siblings of the soldier
(the soldier continued service as Roman citizen to complete his 25 years),
but no wives and kids are mentioned - Eck & Pangerl, Chiron 33, 2003,
347ff

Questions that remain are:

1. Why were children no longer included after 140
AD ?
2. Why did diplomas continue beyond the widening
of the Roman citizenship under Caracalla for Praetorians and Praetorian
Fleets, but not for Auxiliary soldiers ?
3) How about the Roman citizen soldiers serving
in the Legions ?

To question 1 we can assume that the number of such
children may have increased substantially, and maybe Antoninus Pius simply
wanted to clarify situation unfair to the Roman legions, citizen soldiers
for whom we are not aware they got the same privilege of legalizing their
inofficial mistresses and offspring (see question 3).

To question 2 there is no 100% satisfying answer.
Why would Praetorians, and fleet or auxiliary soldiers
already Roman citizens (either by birth or after Caracalla's widening of
the citizenship in 212 AD) still benefit from a military diploma ?
If they married a Roman citizen girl, they certainly had no need for a
diploma.
During the 1st and 2nd centuries - before the wider
impact of citizenship grants to veterans created a sufficient supply of
women with Roman citizenship even in the remotest limes areas - a
soldier
was likely to marry a non-citizen woman, a foreigner or a freed slave
woman. And as we learned above Roman
citizens could not have a formal marriage with non-citizens, and their
children
did not enjoy the full status of a Roman born. Thus as long as there
are non-citizen women to marry, a diploma would make sense, at least
for some.
The termination of auxiliary diplomas around 203
makes somewhat sense in this context. Soldiers could marry during Septimius
Severus, and all free inhabitants of the Empire became Roman citizens anyway
during Caracalla. All men were Roman citizen anyway, and there were no more foreign
women to marry. So far so good.
But auxiliary diplomas became already increasingly
rare already much earlier - after Antoninus Pius (see graph above). And
we still find Praetorian and fleet diplomas after 212 AD. Actually more
than ever. Most Praetorian and Fleet diplomas we know of were issued after
Septimius Severus / Caracalla and fall under this paradox. Why would veterans
still want a diploma ? Honor ? Still for their foreign wives from outside
of the Roman empire ? Or were the Praetorians of that period we know of
mostly coming from outside the Roman borders ? No, most were born
in cities in the balkans, from inside the Roman empire. Hard to explain
!
There must be a reason for this we can only speculate
about. Maybe we misunderstood the widening of the citizenship under Caracalla and it was much more restrictive
?

Thirdly the question about the legionaries, all Roman
citizens, but who might have also enjoyed a marriage with a non-citizen woman,
but who seemingly never got diplomas. And let us remember most legions
were also stationedat the borders
with a chronic undersupply of Roman citizen girls (see above). Still the
only legionary diplomas we know are from the civil
war of 68/69 AD for soldiers of Legio I and II Adiutrix formed out
of auxiliary non-citizen fleet soldiers, who needed to be quickly "Romanized".
No good answer here either.

Why do we find so few diplomas
?

The number of diplomas issued must have been in
the 100,000s over the centuries, but we have so far only found fragments
of a good 1000, far less than 1 %.
Why ?
Bronze was a costly resource that could be readily
reused, either by melting it down as scrap metal, or by finding other use.
Some examples below:

Not all that is bronze and carries
a military discharge text is a citizenship diploma...

A Military Discharge Diplomanot granting citizenship and not
officially witnessed and sealed (likely private copies of official documents in perishable materials such as wood/wax/paper)

under Philippus I and II, from the
RGZM Mainz, only one side with text, likely a private bronze copy of a
letter